The present invention relates to three-dimensional fabrication and, more particularly, to a method and system for three-dimensional fabrication of objects having enhanced dimensional accuracy.
Three dimensional fabrication processes are defined as processes in which objects are constructed in layers utilizing a computer model of the objects. The layers are deposited or formed by a suitable device which receives signals from a computer using, e.g., a computer aided design (CAD) software.
Three-dimensional fabrication is typically used in design-related fields where it is used for visualization, demonstration and mechanical prototyping. Thus, three-dimensional fabrication facilitates rapid fabrication of functioning prototypes with minimal investment in tooling and labor. Such rapid prototyping shortens the product development cycle and improves the design process by providing rapid and effective feedback to the designer. Three-dimensional fabrication can also be used for rapid fabrication of non-functional parts, e.g., for the purpose of assessing various aspects of a design such as aesthetics, fit, assembly and the like. Additionally, three-dimensional fabrication techniques have been proven to be useful in the fields of medicine, where expected outcomes are modeled prior to performing procedures. It is recognized that many other areas can benefit from rapid prototyping technology, including, without limitation, the fields of architecture, dentistry and plastic surgery where the visualization of a particular design and/or function is useful.
In the past several years, there has been considerable interest in developing computerized three-dimensional fabrication techniques.
One such technique is disclosed, e.g., in U.S. Pat. Nos. 6,259,962, 6,569,373, 6,658,314, 6,850,334, 6,863,859 and 7,183,335, U.S. Patent Application Publications Nos. 20050104241 and 20050069784, and PCT Publ. No. WO/2004/096527, the contents of which are hereby incorporated by reference. In this technique, an interface material is dispensed from a printing head having a set of nozzles to deposit layers on a supporting structure. Depending on the interface material, the layers are then cured using a suitable curing device. The interface material may include build material, which forms the object, and support material, which supports the object as it is being built.
In another such technique, disclosed, e.g., in U.S. Pat. No. 5,204,055, a component is produced by spreading powder in a layer and then depositing a binder material at specific regions of a layer as determined by the computer model of the component. The binder material binds the powder both within the layer and between adjacent layers. In a modification of this approach, the powder is raster-scanned with a high-power laser beam which fuses the powder material together. Areas not hit by the laser beam remain loose and fall from the part upon its removal from the system.
U.S. Pat. No. 6,193,923 to Leyden et al. discloses a selective deposition modeling system which includes a dispensing platform slidably coupled to an X-stage. A multi orifice inkjet head is located on the dispensing platform and configured for jetting hot melt inks onto a part-building platform. The dispensing platform moves back and forth in the X-direction relative to a part-building platform, such that the inkjet head scans the part-building platform while jetting the inks thereon. The head is computer controlled so as to selectively activate its orifices and cause them to simultaneously emit droplets of ink in a configured pattern corresponding to the shape of the object.
Leyden et al. contemplate several building styles, including dispensing higher drop density in down-facing surfaces, up-facing surfaces or boundary regions of the object compared to interior regions of the object; and building down-facing and up-facing skin regions which respectively extend several layers near down-facing and up-facing surfaces.
Another reference of interest is U.S. Published Application No. 20040159978 to Nielsen et al., which discloses a technique for reducing the effects of “terracing” in a three dimensional fabrication processes. The terracing effect leaves noticeable visual traces, typically in objects that have vertically contoured surfaces which spread across multiple layers. To overcome this effect Nielsen et al. vary the amount of binder or build material added across each layer, such that the thickness of the layer is gradually decreased in transition regions between successive terraced layers.
Also of interest is a three-dimensional fabrication technique known as stereolithography, disclosed, e.g., in U.S. Pat. No. 4,575,330. In this technique, a focused ultra-violet (UV) laser scans the top of a bath of a photopolymerizable liquid material. The UV laser causes the bath to polymerize where the laser beam strikes the surface of the bath, resulting in the creation of a solid plastic layer just below the surface. The solid layer is then lowered into the bath and the process is repeated for the generation of the next layer, until a plurality of superimposed layers forming the desired part is obtained.
Even though three-dimensional fabrication is widely practiced and has become a routine process for manufacturing three-dimensional objects, it is not without certain operative limitations that would best be avoided.
For example, in conventional three-dimensional fabrication techniques there is a discrepancy between the designed thickness and the final thickness of the deposited layers. The discrepancy may be the result of various factors, including continuous shrinkage process, incompatibility between the resolution of the layer and its thickness, formation of “dead” areas in the layers and the like. This discrepancy oftentimes leads to a reduction in the accuracy of the final product.
Additionally, many of the presently known three-dimensional fabrication techniques employ a leveling device which ensures that each layer of the object is accurately leveled, but, at the same time, discards excess material from the layer and a considerable amount of waste is produced at each leveling step.
There is thus a widely recognized need to have a method and system for three-dimensional fabrication, devoid of the above limitations.